Convection in a Fish Tank
2008; Taylor & Francis; Volume: 75; Issue: 1 Linguagem: Inglês
ISSN
1943-4871
Autores Tópico(s)Fluid dynamics and aerodynamics studies
ResumoAs a high school science teacher with limited funds, I am always looking for demonstrations that are both cost-effective and visually stimulating. This demonstration is more captivating than a lava lamp and is a great method of modeling convection using materials most science teachers already have at home or in the classroom. Understanding convection is fundamental for students to fully grasp the science behind large-scale events on Earth, such as global wind patterns, plate tectonic movement, ocean current patterns, and hydrothermal vent dynamics. Convection can also help students understand how car engines are cooled, how radiators heat a room, how a pot of water boils, and how lava lamp fluid moves up and down. Using a convection demonstration in a classroom emphasizes the importance of convection while captivating students' interest. Materials and directions The following materials are needed for you to lead the convection demonstration: * one 10 gal (38 L) fish tank * two dictionaries or two stacks of magazines, 5-7 cm high * 100 pennies * three tea light candles * bottle of red food coloring * bottle of blue food coloring * water * matches Place the two dictionaries 20-25 cm apart on a flat surface and set the fish tank on the dictionaries (Figure 1a). Make sure that the tank is stable, level, and not hanging off the sides of the books. Place the 100 pennies in rows across the center of the tank. Make the first layer three rows wide, then stack two additional rows of pennies on top of the first layer of coins. The second and third layers of pennies should be stacked to overlap the gaps between the bottom pennies (Figure 1b). This creates a groove between the pennies in the top two rows that will help hold the food coloring in place. Fill the tank with water to about 5 cm from the rim of the tank. Place the candles in a line below the fish tank directly under the pennies. Take the bottle of red food coloring in hand and, with minimal disruption to the water, move your hand to the bottom of the tank and slowly squeeze the red food coloring into the groove made by the pennies. (If done correctly, the food coloring will stay resting on the pennies, see Figure 1c.) Stop squeezing the bottle and slowly remove your hand and the bottle from the fish tank, trying to disturb the water as little as possible. After the water settles, light the candles under the fish tank. The demonstration is ready to begin (Figure 1d). Within one minute after being lit, the candles will heat the pennies and start the process of convection. The hot pennies heat the water and the expanded, less dense water begins to rise away from the heat source. The red food coloring colors the heated water, allowing students to see the water rise. The red color represents the hot, less dense water rising (Figure 1e). As the heated water and red food coloring rise away from the pennies, the red-colored liquid is still hot, but it begins to cool as it moves away from the pennies. The red-colored liquid cools down and spreads out as it continues to move up, away from the heat source (Figure 1f). [FIGURE 1a OMITTED] [FIGURE 1b OMITTED] [FIGURE 1c OMITTED] [FIGURE 1d OMITTED] [FIGURE 1e OMITTED] [FIGURE 1f OMITTED] [FIGURE 1g OMITTED] [FIGURE 1h OMITTED] [FIGURE 1i OMITTED] Place two drops of blue food coloring in rapid succession 2-4 cm from both sides of the rising red food coloring (Figure 1g). The blue food coloring represents the cooled, dense water descending back to the depths of the fish tank. The dense blue liquid will be pushed away from the center of the tank by the laterally moving, cooling red water at the upper portion of the tank. …
Referência(s)